Lithography is used to produce micro- and nanostructured components, such as integrated circuits, for example. The lithography process is carried out via a lithography apparatus comprising an illumination system and a projection system. The image of a mask (reticle) illuminated via the illumination system is in this case projected via the projection system onto a substrate (for example a silicon wafer) coated with a light-sensitive layer (photoresist) and arranged in the image plane of the projection system, in order to transfer the mask structure to the light-sensitive coating of the substrate.
Therefore, projection or used light is used for imaging a lithographic structure onto the image or wafer plane. The aspiration to achieve ever smaller structures in the production of integrated circuits is currently driving the development of EUV lithography apparatuses that use projection or used light having a wavelength in the range of 0.1 nm to 30 nm, in particular 13.5 nm. In the case of such EUV lithography apparatuses, because of the high absorption of light of this wavelength by most materials, reflective optical units, that is to say mirrors, are used instead of—as previously—refractive optical units, that is to say lens elements.
In the case of such small structures it can be important to achieve a high imaging quality. This also applies in particular to processes with multiple exposures. For this reason, any fault sources that contribute to an impairment of the imaging are desirably taken into consideration and at best eliminated. Typical imaging aberrations can be minimized via adaptive optical units, for example. Vibrations, in particular, can have a great influence. They can arise in all regions of a lithography apparatus itself, for example as a result of flowing cooling water or airstreams and also as a result of human activity in the building or as a result of traffic in the vicinity. Vibrations can have the effect of causing optical elements themselves to oscillate, wherein for example the surface thereof can deform, which adversely affects the properties of the optical element. Particularly in the case of mirrors, faults of this type can have a double effect since an error in the angle of incidence induces an error of identical magnitude in the angle of reflection.
There are various measures for mechanically decoupling sensitive components or assemblies, for example the projection optical unit of a lithography apparatus, from the environment. However, in the case of adaptive optical units both control signals are transmitted for components, such as actuators or sensors, between the optical unit and an external controller and a supply voltage to the active components. Signal and power lines are used for this. Depending on the desired properties of the lithography apparatus, the line cables are insulated and/or shielded. Particularly in the case of signal lines it is desirable to shield the lines from unwanted influences in order to ensure an error-free signal transmission. This is achieved for example via a multilayered construction, as in the case of multiply shielded signal lines or coaxial cables. Such a multilayered construction of a cable can lead to a not inconsiderable stiffness of the cable. Such a stiff cable can also produce a mechanical coupling of an outer frame to the projection optical unit or the various active components. A large number of controllable components can involve a correspondingly large number of cables, which correspondingly amplifies the mechanical coupling. By way of example, four cores are used for a connection according to USB 1.0 specification: Ground, +5V, data+, data−. The USB 3.1 specification already stipulates 24 cores combined for example in a cable. The more cores a cable has, the stiffer it can become. Correspondingly there can also be an increase in a mechanical coupling strength over the cable. The mechanical coupling likewise can increase if a plurality of cables are used.
One possibility for reducing the number of cables involves wireless communication. For this purpose, however, all mechatronic components are desirably equipped with a corresponding receiver. This type of data transmission can be more susceptible to interference in comparison with cable-connected systems. Furthermore, the data transmission rate can be limited to a greater extent. Finally, a power supply is typically used for these systems as well, and so at least a certain number of wired transmissions are typically present.
Known cable-connected systems use for example cable loops and longer cables than necessary in order to reduce the transmission of vibrations via the cables. In order to realize a low mechanical coupling, for example the cable length is chosen depending on a cable stiffness. However, this approach can involve a correspondingly large space and is therefore not always able to be used.